North America and Europe combined have fewer square kilometers of surface area than the Moon: 36.8 million for the two continents versus 37.8 million for Earth's natural satellite. In August-September 1992, at the 43rd Congress of the International Astronautical Federation (IAF) in Washington, DC, Madhu Thangavelu, a research associate at the University of Southern California's Institute of Aerospace Systems Architecture and Technology, argued that explorers operating from a fixed surface base — the traditional advanced lunar exploration scenario — could hope to survey only a small fraction of the lunar surface. Moreover, only after several costly piloted lunar landing missions had investigated candidate sites could a single fixed base site be selected.
At the time Thangavelu presented his paper, the Space Exploration Initiative (SEI), launched by President George H. W. Bush on the 20th anniversary of the first piloted Moon landing (20 July 1989), was nearing its end. Though at SEI's start NASA had proposed a traditional fixed-site permanent lunar base concept, by the time of the 1992 IAF meeting it had shifted its attention to a temporary lunar outpost concept called First Lunar Outpost (FLO). NASA made the change based on recommendations in the May 1991 report of the SEI Synthesis Group (the Stafford Committee).
Thangavelu did not mention FLO in his paper, though he might have noted that it had many of the limitations of the fixed-site base scenario. In its most basic form, FLO would see a series of 45-day piloted lunar missions, each employing one Habitat Lander and one Crew Lander. FLO astronauts would have at their disposal roving vehicles not too different from the jeep-like Apollo rovers. These would permit traverses of at most a few tens of kilometers from their temporary lunar outpost.
Thangavelu suggested that NASA replace the fixed-site lunar base approach with a "roving base" that would, in a single ambitious piloted mission, explore multiple candidate base sites and the terrain between them along an 11,000-kilometer traverse route. He called his roving base Nomad Explorer.
The chief element of the Nomad Explorer roving base was the 35-tonne Very Long Traverse Vehicle (VLTV), which would measure 16 meters long, 4.5 meters wide, and 10 meters high. The VLTV would roll on four large wheels, each powered independently by a 120-horsepower electric motor. The complex wheels would change shape automatically to accommodate obstacles and ensure a smooth ride. Typically, the VLTV would move at about 20 kilometers per hour, though it could trundle along at up to 30 kilometers per hour if necessary.
The VLTV would provide its three-person crew with 600 cubic meters of pressurized volume. It would include a control cockpit, crew quarters, a meeting room/galley, an airlock, and a hygiene facility.
Life support water tanks and stacked bags containing lunar dirt on the vehicle's roof would partially shield against solar flare and galactic cosmic radiation. A periscope-like assemblage of mirrors and baffles would provide the driver with an elevated view of the surface while blocking some radiation; along with movable cameras and floodlights, it would augment a more conventional "windshield" with sloping tinted windows directed toward the surface.
Thangavelu proposed a novel system for providing the Nomad Explorer roving base with electricity — an automated "power cart" bearing a nuclear reactor that would follow about a kilometer behind the VLTV to limit crew radiation exposure. It would supply 50 kilowatts of electricity to the piloted rover either through a long durable cable or through intermittent microwave beaming. An auxiliary fuel cell/solar cell system on the VLTV would provide 10 kilowatts of backup electricity.
The most novel feature of Thangavelu's Nomad Explorer design was, however, the EVA Bell, an accordion-like structure that would extend down from the VLTV's underside. Thangavelu intended that the 48-cubic-meter EVA Bell should eliminate what he considered to be the worst feature of moonwalks: the need for bulky space suits. Space suits, he explained, decreased astronaut mobility and dexterity, caused fatigue, and required excessive time for donning. The EVA Bell would also protect the astronauts from abrasive lunar dust.
In addition to the EVA Bell, the VLTV would include two robot arms that could stand in for or assist space-suited astronauts. These would ride on tracks on the VLTV's exterior, enabling them to reach out from the rover in any direction.
The Nomad Explorer roving base would, of course, require a supporting space transportation infrastructure. Thangavelu envisioned a revived Saturn V rocket which he called the "Saturn V-B." This would launch Autonomous Modular Common Landers (AMCLs) configured for either automated or piloted operation. Though he did not mention it, NASA's proposed FLO launch vehicle, informally dubbed the "Saturn VI," might have stood in for the Saturn V-B with modest uprating or if used in an Earth-Orbit Rendezvous architecture. Uprated, modified FLO Crew and Habitat Landers might have replaced the AMCLs.
An automated AMCL would land the Nomad Explorer roving base at the start of its planned traverse route. Others would land supplies and experiment payloads no more than 3000 kilometers apart along the route. A one-way piloted AMCL would deposit the VLTV crew near the roving base at the starting point of the long traverse, and an automated AMCL bearing a crew Earth-return vehicle would land at the end of the traverse route.
The astronauts would then begin their six-month journey across the Moon's rolling, dusty terrain. Upon reaching the first resupply AMCL, they would use the VLTV's robot arms to transfer supplies it carried to a special port on the VLTV, then would put the EVA Bell into action. First, they would use the VLTV's robot arms to spread a "mat" on the lunar surface. The crew would then use the arms to transfer a site-specific scientific payload from the AMCL to the center of the mat.
Next, the astronauts would position the VLTV so that it straddled the payload. They would extend the EVA Bell, which would lock onto the mat, forming an air-tight seal. The astronauts would fill the EVA Bell with air, then would climb down into it to deploy the payload. After they completed their tasks, they would exit the EVA Bell, pump out its air, and raise it off the mat, exposing the payload to lunar surface conditions.
In addition to scientific instruments, the astronauts would deploy a telecommunications network for future operations as they moved over the lunar surface. Upon reaching the end of their traverse, they would place the Nomad Explorer roving base in "hibernation." They would then board the pre-landed AMCL Earth-return vehicle and blast off for home.
"The Nomad Explorer Assembly Assist Vehicle: An Architecture for Rapid Global Lunar Infrastructure Establishment," IAF-92-0743, Madhu Thangavelu; paper presented at the 43rd Congress of the International Astronautical Federation, 28 August-5 September 1992, Washington, DC.